As top boxes I'm going to make a DIY MID HIGH, a 2x 12" BPH loaded Mid bass and a 1.4" coax BMS driver. Link here:https://soundforums.net/forum/low-earth-orbit/diy-audio/11601-new-diy-mid-high

So I was on a quest of some bass boxes to be able to follow these tops.I wanted a system that is reasonably sized and a one man lift, after testing different drivers my eye fell on the BMS 18n862, as it gives the response I was after in the right sized box, The Singing Canary was born!Per side i want 3 bassboxes vs 1 topbox.

This is the first time I'm designing a reflex box, so it would be nice to have some feedback from more experienced designers.

Sizes are 50 x 55 x 93.5 cm so two can fit in my car.

I didn't draw the 3 bassreflex tubes yet, as my skills on SketchUp are limited. They obviously start at the front of the box, at the back of the box they make a 90degree turn up till the highest board with three holes. In total the tubes are just a little shorter as 1 meter.Also not drawn are the round flares I will make at both ends of the tube te reduce turbulation. The flares will have a r of 3cm (20% of the 14cm diam. of the tube).I paid extra attentions to bracing, especially because this box can drop low and can produce serious SPL levels. All outside panels will be Birch ply, but on the inside i wanted to used a lighter pine wood to save some weight.

After experimenting 3 tubes with a diameter of 14cm gave me the least air velocity. 28m/s at 1500W is the best I could achieve while still be able to fit the tubes in the box.Is this figure acceptable?

this is the response with a Q2 filter on 28.5Hz applied.

Vb is 153 Liters, the ports take up 46 Liters, bracing and the speaker 15.5 Liters, So the total volume of the box is 214.5 Liters

Cone excursion... Here I would like some input, the BMS 18n862 has a Xmax of 19mm, the Xlim is unknown to me. At 1500W the speaker goes slightly over Xmax at 40Hz and more at 20Hz.Is this acceptable? Or is this maybe too conservative because the probably the Xlim isn't in reach yet?

The filters I applied:

Before making the actual speakers I'm going to make a prototype, so I can measure the impedance and tune the speaker precisely accordenly.

Please share your thoughts...Once the box is tested I'll draw up complete plans and will share it here with the community.

With a quick glance it looks very good, full width slot ports may help with cooling if used for all night EDM. Bracing looks really good. no need to countersink the driver on the baffle, just weakens it, also how is the grill going to be fitted?

Looks like your going to have a tasty little system - little in size only

You guess that the coils will burn with an SAE PCM 20 at full tilt on 4 speaker?Would you suggest to use no EQ at all? Or do you have a golden amount.Without EQ the box will need to be 330L to go as deep... Thats starting to get out of my comfort zone.

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